Wheat is grown worldwide and is the most widely adapted cereal. There are five main wheat market classes. They include the four common wheat (Triticum aestivum L.) classes: hard red winter, hard red spring, soft red winter, and white. The fifth class is durum (Triticum turgidum L.). Common wheats are used in a variety of food products such as bread, cookies, cakes, crackers, and noodles. In general the hard wheat classes are milled into flour used for breads and the soft wheat classes are milled into flour used for pastries and crackers. Wheat starch is used in the food and paper industries, as laundry starches, and in other products. Because of its use in baking, the grain quality of wheat is very important. To test the grain quality of wheat for use as flour, milling properties are analyzed. Important milling properties are relative hardness or softness, weight per bushel of wheat (test weight), siftability of the flour, break flour yield, middlings flour yield, total flour yield, flour ash content, and wheat-to-flour protein conversion. Good processing quality for flour is also important. Good quality characteristics for flour from soft wheats include low to medium-low protein content, low water absorption, production of large-diameter test cookies and large volume cakes. Wheat glutenins and gliadins, which together confer the properties of elasticity and extensibility, play an important role in the grain quality. Changes in quality and quantity of these proteins change the end product for which the wheat can be used.
Rhizoctonia root rot. Rhizoctonia root rot is an important, yield-limiting disease in direct-seed wheat production systems. Under severe disease pressure, plants are stunted, creating bare patches in the field that can severely limit grain yield. Pathogenic Rhizoctonia and Pythium are endemic throughout the Pacific North West (PNW) of the United States and in cereal production regions in Australia and throughout the world. Disease pressure by these pathogens is also dependent upon soil type, moisture, temperature and other abiotic and biotic factors. If direct-seed systems are to succeed in the PNW and other areas where Rhizoctonia root rot is a problem), varieties adapted to reduced tillage or direct seed environments, and associated diseases, must be developed. Significantly, despite considerable effort, no naturally occurring Rhizoctonia resistant wheat plants have been identified to date (Smith, J. D., K. K. Kidwell, M. A. Evans, R. J. Cook and R. W. Smiley. 2003a, Assessment of spring wheat genotypes for disease reaction to Rhizoctonia solani AG-8 in controlled environment and direct-seeded field evaluations, Crop Science 43:694-700; Smith, J. D., K. K. Kidwell, M. A. Evans, R. J. Cook and R. W. Smiley. 2003b, Evaluation of spring cereal grains and wild Triticum germplasm for resistance to Rhizoctonia solani AG-8, Crop Science 43:701-709). Moreover, although differences in disease response to Rhizoctonia root rot have been detected among adapted spring wheat varieties, all varieties tested to date are susceptible (Smith, J. D., K. K. Kidwell, M. A. Evans, R. J. Cook and R. W. Smiley. 2003a, Assessment of spring wheat genotypes for disease reaction to Rhizoctonia solani AG-8 in controlled environment and direct-seeded field evaluations, Crop Science 43:694-700). Furthermore, a survey of a sub-sample of wild relatives of wheat also failed to identify a suitable resistance gene donor for Rhizoctonia root rot (Smith, J. D., K. K. Kidwell, M. A. Evans, R. J. Cook and R. W. Smiley. 2003b, Evaluation of spring cereal grains and wild Triticum germplasm for resistance to Rhizoctonia solani AG-8, Crop Science 43:701-709).
Mutation Breeding. Mutation Breeding comprises the use of chemical mutagenesis to increase genetic diversity. Natural mutations arise due to errors in replicating DNA. Such mutations are exploited when they are introduced from wild relatives of crop plants. The error rate during DNA replication is increased by treatment of plant seeds with chemicals called mutagens, and this chemical mutagenesis is a tool for increasing the variation in a plant population. Chemical-induced variants are currently accepted as an alternative to “Genetically Modified” plants made by transformation. Over 2,250 crop varieties now in use come from mutation breeding (M. J. Chrispeels and D. E. Sadava 2003, Plants, Genes, and Crop Biotechnology (2nd edition), Jones and Bartlett Publishers (Boston). Currently, for example, the herbicide-resistant Clearfield Wheat is a well-known example of a wheat variety from mutation breeding.
There is a pronounced need in the art for root rot resistant plants (e.g., wheat). There is a pronounced need in the art Rhizoctonia root rot resistant plants (e.g., wheat). There is a pronounced need in the art for novel methods for generating such resistant plants. There is a pronounced need in the art for novel methods comprising mutation breeding used to address the major problems that occur in wheat production (e.g., Rhizoctonia root rot).